Continuing studies on the molecular biology of latent herpes simplex virus (HSV) infection in nerve ganglia have demonstrated a polyadenylated viral transcript which appears to be expressed throughout the period of latent infection. This viral transcript was accurately mapped to a region of the HSV genome where only one other gene, the immediate early 1 gene, is known to map. This important finding extends our knowledge of the state of the virus during latency and allows formulation of a hypothesis for the molecular basis of latent HSV infection. Ongoing studies in mice with a recombinant vaccinia virus vaccine for herpes simplex have demonstrated that immunity against HSV is increased by a booster dose of the vaccine but decreased by previous exposure to vaccinia. A newly constructed double recombinant vaccinia vaccine expressing antigens from both HSV and influenza A was tested in mice and induced antibodies and protection against challenge with either influenza A or HSV. Clinical studies examining the ability of acyclovir to prevent ultraviolet light-induced reactivation of HSV have continued and a new study examining the ability of daily oral acyclovir to block recurrences of herpes labialis was initiated. Previous studies with lactate dehydrogenase virus have indicated that impairment of enzyme clearance is a more important factor than previously suspected in the regulation of serum enzyme levels. Studies over the past year have examined an important step in enzyme clearance, and the binding of enzymes and other proteins by macrophages. A technique for measuring enzyme binding was established and studies examining the binding of lactate dehydrogenase and other proteins were initiated.